weird Ruby 1.8.7 syntax error
don't reuse outdated pull request messages

Prior to a53f028, hub didn't clean up PULLREQ_EDITMSG files after a successful
pull request. When people upgrade to the new version of hub which reuses PR
messages, these leftover files will get reused when opening new PRs and will
lead to confusion. The hackish solution is to ignore PULLREQ_EDITMSG files that
are older than the hub ruby script on disk.